Straight from Microsoft, the Silverlight Toolkit provides the developer community with new components, functionality, and an efficient way to help shape product development. Toolkit releases include open source code, samples & docs, plus design-time
support for the Silverlight browser plugin.

Windows Phone Toolkit – Starting October 30th 2012 – Windows Phone toolkit will have a new home under
http://phone.codeplex.com to better manage Windows Phone specific codebase and issues.